The invention relates to a process for uniform and fast heating of microwaves that are pulsed and introduced intermittently into the products which are conveyed through a treatment chamber in which the pulsed energy is supplied.
A process of this general kind is disclosed in U.S. Pat. No. 4,956,530, which discloses a treatment chamber, a continuous conveyor belt for conveying articles through the chamber, microwave input channels, and microwave generators for supplying microwave energy to the articles. U.S. Pat. No. 4,956,530 is hereby incorporated by reference for disclosure of those features, which per se form no part of the present invention.
By means of a pulsed and intermittent supply of the microwave energy required for increasing the temperature up to a certain level, it is ensured that the product surface is not excessively heated. The microwave power may assume various forms, with a rectangular form having the strongest effect on the product surface. Given a pulse-type operation of the line, however, trapezoidal and sinusoidal forms of power also lead to satisfactory results.
When lines that operate at 2,450 gigahertz are used, the long build-up time per pulse adversely influences the heating-up time, which means that relatively little energy can be introduced per energy supply pulse as a higher energy supply per pulse would damage the product surface.
A pulsed and intermittent introduction of energy into the products to be treated is expedient as the amount of microwave energy supplied (power.times.time) would otherwise be too high relative to the capacity of absorption of the product in a given length of time, thereby leading to an excessive and critical temperature increase at the product surface. If the energy supply is pulsed, microwave energy is repeatedly introduced into the product for a determined length of time.